What were the first organisms to have sex? We may never know the answer, but as Bill Nye explains in this Big Think interview, scientists are very interested in why sexual activity remains so popular in nature...

“I think it is a very personal decision," said Dr. Juan Troncoso of the Johns Hopkins Alzheimer's Disease Research Center during Big Think's recent Breakthroughs: Alzheimer's panel discussion. "Some people may not want to do it. Others who are very practical for planning reasons may want to do it.”

There isn’t a single gene that causes Alzheimer’s disease, yet the gene Apolipoprotein E (APoE) has been implicated as a risk factor for the disease. People with APoE E4—a version of the gene with an E4 allele—are three to eight times more likely to develop Alzheimer’s than those with a different ApoE allele (E2 or E3). The E4 allele is present in about 25 to 30 percent of the population. Importantly, having ApoE E4 doesn't automatic mean a sentence of Alzheimer's disease, and many people with the disease do not have the allele. Yet, as genetic testing becomes more common, APoE will be where genetic tests look for the risk of this debilitating disease that currently doesn't have a cure.

Dr. Leonard Guarente of the Glenn Laboratory for the Science of Aging at MIT sees little reason for testing without being able to do something about it. “I would like to know about risk for any disease that can be treated, but for a disease for which there is really no treatment I would rather not know,” he says.

“There is one more twist to this,” says Dr. Tronocoso, “If for some reason you’re going to have a child and you may want to know whether you have a gene that will increase the risk in them.”

Image courtesy of Flickr user jurvetson

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